This invention relates to piezoelectric actuators which employs the linear reciprocal displacement caused by the transverse effect of a piezoelectric element. The invention more particularly relates to an improved sustaining device for strengthening the stiffness of an amplifying system for use with a piezoelectric element.
Referring to FIG. 5, a conventional piezoelectric actuator will be explained. FIG. 5A is a front view and FIG. 5B is a side view drawing of a known piezoelectric actuator. Numeral 1 denotes a frame. Numeral 2 denotes a mechanical amplifying portion. The frame 1 and the mechanical amplifying portion 2 may be press-formed as one unit, preferably from a material such as spring steel. Numeral 5 denotes a hole which may be drilled in the frame 1 and used for actual installation.
The mechanical amplifying portion 2 comprises a first lever 2a and a second lever 2b, thus configuring a double step amplifying mechanism. Fulcrums 3a, 3b, 3c are equiped with elastic hinges of springs.
A piezoelectric element 4 is inserted between an end 2c of the first lever 2a at the mechanical amplifying portion 2 and a flat inside surface 1a at the lower side wall of the frame 1. The piezoelectric element 4 may be bonded in position with Araldite (tradename).
Under the above described configuration of the actuator, when electric voltage is applied to the piezoelectric element 4, since one end of the piezoelectric element is fixed, a transverse effect generates in the direction of the lower arrow in FIG. 5a. The end 2c of the mechanical amplifying portion 2 is thereby pushed up and displaced. This displacement is transmitted to the mechanical amplifying portion 2 where it is amplified and displaces a transmitting arm 6 in direction of the upper arrow.
In this case, the displacement is amplified by the lever length, measured from fulcrums 3a, 3b and 3c respectively, where c=length from 3a to 3b, d=length from 3b to 3c, e=length associated with fulcrum 3c and f=length from fulcrum 3c to transmitting arm 6, and the displacement by the mechanically amplifying portion 2 is expressed as follows: ##EQU1##
As the above formula indicates, the displacement is amplified by the length of lever measured from fulcrums 3a, 3b, and 3c, respectively.
By deenergizing the electric voltage at the piezoelectric element, displacement at the mechanical amplifying portion 2 is declined and the amplifying portion resumes its original position.
In conventional actuators employing a piezoelectric element, if elastic hinges or springs are applied at the fulcrum points of the mechanical amplification portion 2, the actuator will work fine, for example, in the case of a dot printer whose function is to utilize impulse power. However, if the actuator is used in a functional mechanism where some resisting loads are applied during transmission of displacement to an outside member (for instance, for displacing another movable part), hinges and springs are torsioned and deformed and the expected displacement may not be achieved.
It is therefore an object of the invention to solve the aforementioned problems by providing a mechanical amplifier for a piezoelectric actuator which increases the strength of the amplifier system.
It is a further object of the invention to provide a piezoelectric actuator and amplifier which are strengthened and may be used for a variety of mechanical applications.